Efficient separations of certain types of cells from complex mixtures has important applications in blood and blood component transfusions, cancer therapies, auto immune diseases and diagnostics. Cell separation devices employed in these separations have been used in extracorporeal circuits to selectively isolate, augment and/or reintroduce to the host a specific subset of cells. Separation processes may be used to remove a subset of cells from the mixture of interest ("negative selection") or to prepare a specific subset of interest from a mixture (positive selection). In negative selection, the cells to be discarded remain in the device. In positive selection, desired cells initially remain in the device while the undesired cells and other contaminants flow through and are removed. The desired subset is subsequently obtained as a more pure fraction from within the device.
Blood and lymph fluids provide the medium through which red blood cells, white blood cells (leukocytes), nutrients, metabolites, growth factors, hormones, antibodies, and the like are transported from one site in the body to another to enable production of various compounds by cells and tissues for regulation of other cells and tissues. Additionally, these same fluids remove waste materials to prevent the accumulation of harmful compounds. Blood and lymph fluids also transport cells of the hematopoietic system throughout the body to allow fulfillment of a variety of functions. At the same time, a wide variety of materials are transported to the cells of the hematopoietic system for processing or for inducing a cellular response, as in the case of formation of antibodies to counteract antigens, pathogens, and the like. Thus, interaction between hematopoietic cells and blood can provide useful information about the disease-states in individuals, creating significant interest in the potential therapeutic value of accessing these fluids to manipulate various components related to or present in the blood stream.
Blood is a complex mixture that is known to change in response to foreign environments. When blood or components thereof are not intended for reuse, this may not pose any problems. However, when blood or components thereof have to be returned to the host, such changes could be detrimental. For example, in plasmapheresis or transfusion therapy, it is desirable to restore a person's blood. However, due to uncertainties concerning the safety of the blood supply due to viruses such as cytomegalovirus (CMV), hepatitis, HTLV-1, HIV, or the like, such return to the host may be precluded.
Transfusion of packed cells or whole blood containing donor leukocytes to a recipient can be harmful. For example, transfused leukocytes can cause Graft versus Host (GVH) disease in which the transfused leukocytes cause irreversible damage to the blood recipient's organs in immuno compromised patients. Red cell transfusions can adversely affect the survival of patients undergoing colo rectal cancer surgeries. This effect is believed mediated by the transfusion of components other than donor red blood cells including the donor's leukocytes. At a recent meeting of the American Association of Blood Banks (ABBE Meeting, Florida, 1993) studies were presented which showed that patients who received leukocyte depleted blood, when compared to those who did not, had fewer returns to the hospital following a surgical procedure.
Known cell separations involve several techniques, some of which are based on specific affinities. Other cell separation techniques rely on more serendipitous mechanisms such as entrapment of target cells in supports of various origins and structures. See, for example, Wigzell and Anderson, J. Exp. Med. 129:23-36, 1969; Rutishauser et al. Proc. Natl. Acad. Sci. 70, 1973; Wysocki and Sato, Proc. Natl. Acad. Sci. 75:2844-2848, 1978; Antoine et al. Immunochem. 15, 1987. See also, U.S. Pat. Nos.: 4,230,635; 4,363,634; 4,617,124; 4,619,904; 4,880,548; 4,925,572; 4,963,265; 5,215,926; and 5,240,856. The basic process of affinity separation entails creating contact between cell mixtures to be separated and a support matrix to enable the target cells to preferentially attach, bind, adsorb or become trapped to and within the support, and then washing away the undesired cells, or vice versa. Specific affinity techniques use monoclonal antibodies to recognize specific markers on the membranes of cells and to "attract" the target cells to bind to the monoclonal antibodies. Specific affinity "attractions" of target cells also may occur by hydrophobic or hydrophilic interactions, metal-affinities, ion exchangers, and the like.
Given that some form of health care reform in the United States is highly likely, it is of great interest to develop practical and cost-effective procedures and equipment which will enable removal and/or recovery of cells to provide increasingly higher yields and purity levels irrespective of scale. Attempts to scale-up separation procedures, however, have not proven practical. One successful approach to potential large-scale cell separations so far has involved the use of magnetic particles. However, the use of magnetic particles is expensive.
Scale-up beyond laboratory size has involved either columns packed with beads of a particular type and size, with or without specific chemistries, or the use of compressed stacks of membranes. Unfortunately, mechanisms governing the performance of a column packed with relatively uniform packed beads on the one hand, and membranes on the other, are at the opposite ends of the spectrum as to mass transfer rates and capacities. Surprisingly, it is not until my invention that the apparently mutually exclusive parameters described above, have successfully been combined in to one device.